Heat recovery system including a dual pressure turbine

ABSTRACT

Heat recovery systems are useful, for example, in vehicles that generate large amounts of heat energy during operation. The heat energy is used to drive a turbine that produces useful work. In order to fully utilize the great majority of the heat energy produced, the engine exhaust is used to convert a fluid to a gas and superheat the gas to a preselected temperature at a preselected pressure. If the fluid entering the heat exchanger in the exhaust system is to cool, soot collects on the heat exchanger thus greatly reducing system efficiency. Also various oxides precipitate out of the exhaust and chemical attack the elements in the exhaust system. The present heat recovery system utilizes the heat energy from the oil cooling system to preheat all of the fluid before it reaches the exhaust system. Furthermore, the heat energy from the jacket water of the engine is used to convert a portion of the preheated fluid to a gas. The system converts the remaining portion of fluid to a gas and superheats the gas to a higher preselected temperature. A first stage of a dual pressure turbine receives the superheated gas and directs the gas at a supersonic velocity against the blades of the rotor. The gas exiting the first stage and the superheated gas at a lower preselected temperature is controllably and substantially separately directed to a second stage at substantially the same velocity.

TECHNICAL FIELD

This invention relates generally to a heat recovery system adapted touse the heat produced by by engine to generate a gas that issubsequently used to drive a dual pressure turbine for producing usefulwork and more particularly to the components of the system and theirinterrelationship coupled with the structure of the dual pressureturbine.

BACKGROUND ART

Heat recovery systems are provided in a system to take full advantage ofthe total energy being produced by an engine. A large amount of energyproduced in an engine is lost through the exhaust system and jacketwater cooling. Many of the known heat recovery systems use various formsof heat exchangers in the exhaust system to convert the heat in theexhaust to a form that subsequently performs useful work. Thesteam-based Rankine bottoming cycle heat recovery principle is wellknown and has the potential to increase total engine performance byutilizing the engine exhaust to perform useful work. One processfrequently used converts water to steam and uses the steam to operatemiscellaneous services, such as heaters, and to drive a steam turbine.One of the major problems encounter when using the engine exhaust systemto convert water to steam is soot fouling of the heat exchanger orboiler that is located in the exhaust system. This soot fouling problemis even more pronounced on systems used in diesel engines. It has beenfound that the soot thickness is strongly dependent on the temperatureof the walls of the tubes in the boiler that are located in the exhaustsystem. Naturally the more tubes that are used coupled with the lowertemperature used in the tubes, the more collection of soot. To optimizea system to accept a 5% loss due to sooting could add 30% to the sizeand cost of a total system.

Another major problem that is associated with the low tube temperaturein the boilers that are located in the exhaust system is the tendencyfor various gases to precipitate out of the exhaust gas due to the lowertube temperature. These gases form oxides that chemically attack thevarious metals in the exhaust system thus shortening their useful life.

Various forms of turbine have been used in the Rankine bottoming cyclesystems. These range from single or multiple stage high pressure tubinesto single or multiple stage low pressure turbines and to a mix of lowpressure and high pressure turbines. The main objectives considered indetermining the type of turbine to use is maximizing performance,controlling the cost versus performance, and controlling total packagesize. It has been generally found that the more stages used in theturbine, the greater the system efficiency. However, both the cost andsize of the turbine increases with an increase in the number of stagesused. Many times the cost of added stages will increase at a much higherrate than that of the system performance.

Of the dual pressure turbines used, some of them direct the highpressure steam to only the high pressure side and the low pressure steamto the low pressure side and subsequently to the outlet port. Thesenormally fail to efficiently use all of the available work in the steamor they have to use many turbine stages thus adding significantly to thetotal cost. Of the other dual pressure turbines used, the exhaust steamfrom the high pressure stage or stages is directed to a mixing chamberwhere it mixes with a low pressure steam and directed into the lowpressure stages. The mixing chamber is primarily provided to ensure thatthe temperature, pressure, and velocity of the steam from the highpressure stage is respectively equalized with the temperature, pressure,and velocity of the low pressure steam priior to entering the lowpressure stages. The mixing chamber that is normally used inreases thesize of the total package and further adds the possibility of unwantedturbulence in the chamber.

The present invention is directed to overcoming one or more of theproblems as set forth above.

DISCLOSURE OF THE INVENTION

In one aspect of the present invention, a heat recovery system isprovided for an engine having a liquid cooling system for transferringheat energy away from the engine and an exhaust system. The systemincludes a first heat exchanger having an inlet port and an outlet portand is located in heat transferring relation to the liquid coolingsystem, a second heat exchanger having an inlet port and an outlet portand is located in heat transferring relation to the exhaust system, anda third heat exchanger having an inlet port and an outlet port and islocated in heat transferring relation to the exhaust system. A source ofpressurized fluid is connected to the first and third heat exchangers. Ameans is provided for preheating the fluid from the source and islocated in the system between the source and the first and third heatexchangers. A first means is provided for controllably directing aportion of the preheated fluid at a preselected pressure to the inletport of the first heat exchanger so that the preheated fluid isconverted to a gas at the preselected pressure and for subsequentlydirecting the gas from the outlet of the first heat exchanger to theinlet of the second heat exchanger so that the gas at the preselectedpressure is superheated to a preselected temperature. A second means isprovided for controllably directing the other portion of the preheatedfluid, at a preselected pressure higher than the preselected pressure ofthe gas from the first means, to the inlet port of the third heatexchanger so that the other portion of the preheated fluid is convertedto a gas at the higher preselected pressure and superheated to apreselected temperature higher than the temperature of the gas from thefirst means. The system further includes a dual pressure turbine havinga high temperature and pressure inlet port connected to the outlet portof the third heat exchanger, a low temerature and pressure inlet portconnected to the outlet port of the second heat exchanger, an outletport connected to a condenser that is adapted to convert the outlet gasto a fluid, and an output shaft adapted to transmit a working force fromthe dual pressure turbine in response to the superheated gases from therespective second and third heat exchangers being directed therethrough.

In another aspect of the present invention, a dual pressure turbine isprovided to generate an output force in response to the flow of a gastherethrough. The dual pressure turbine includes a housing having afirst inlet port adapted for connection with a source of gas at apreselected high pressure level and superheated to a preselected hightemperature. A first stage is defined in the housing and includes afirst rotor chamber, a first rotor having a plurality of blades securedaround the periphery and is rotatably positioned in the first rotorchamber, a first plurality of nozzles interconnecting the first inletport and the first rotor chamber adjacent a preselected number of bladesof the first plurality of blades, and an outlet passage connected withthe first rotor chamber adjacent at least the preselected number ofblades. A second stage is defined in the housing and includes a secondrotor chamber, a second rotor having a second plurality of bladessecured around the periphery and is rotatably positioned in the secondrotor chamber and drivingly connected to the first rotor, a secondplurality of nozzles opening into the second rotor chamber adjacent thesecond plurality of blades and the nozzles are evenly spacedtherearound, and an outlet passage connected to the second rotorchamber. A second inlet port is located in the housing and is adaptedfor connection with a second source of gas at a preselected pressurelower than the preselected high pressure and superheated to atemperature lower than the preselected high temperature. A first passagemeans is provided for connecting the second inlet port with the secondplurality of nozzles so that the gas from the second source of gas issubstantially axially directed to the second plurality of nozzles at apredetermined velocity and a second passage means connects the outletpassage of the first stage with the second plurality of nozzles so thatthe gas from the outlet passage of the first stage is substantiallyaxially and substantially separately directed to the second plurality ofnozzles at substantially the same velocity as the predetermined velocityof the gas from the second source.

The present invention provides a heat recovery system that fullyutilizes the heat generated by the engine to drive a dual pressureturbine to produce useful work. The cooling system or more specificallythe jacket water of the engine absorbs sufficient heat energy and thejacket water is passed through a heat exchanger to convert a fluid to agas and then superheat the gas for effective use in the turbine. Anotherheat source from the engine, such as the oil lubrication system,provides sufficient heat to preheat the fluid before it enters the thirdheat exchanger located in heat transferring relation to the exhaustsystem. This relationship maintains an increased temperature at theinlet port of the heat exchanger thus reducing the sooting problem andthe precipitation of acidic gases. The first and second passage means inthe dual pressure turbine cooperate to ensure that the temperature,pressure, and velocity of the respective gases from the outlet passageof the first stage and the second source are respectively substantiallyequal before entering the second stage. This arrangement eliminates amixing chamber between the first and second stages thus also eliminatingthe possibility of turbulence that could exist in the mixing chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial schematic and digrammatic representation of a heatrecovery system incorporating an embodiment of the present invention;

FIG. 2 is a partial sectional view, illustrating in greater detail, oneof the components shown in FIG. 1;

FIG. 3 is a partial section taken along the line III--III of FIG. 2;

FIG. 4 is an enlarged partial section of one of the nozzles and three ofthe rotor blades of the first rotor of FIG. 2 shown in their trueposition;

FIG. 5 is a partial section taken along the line V--V of FIG. 2; and

FIG. 6 is a section taken along line VI--VI of FIG. 5.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawings, and more specifically to FIG. 1, a heatrecovery system 10 is provided for use on an engine 12 having a liquidcooling system 14 and an exhaust system 16. The liquid cooling system 14includes a pump 18 for circulating cooling fluid through a known waterjacket (not shown) in the engine, a thermostat 20 adapted to control thetemperature of the cooling fluid, and the associated cooling lines 22.The exhaust system 16 includes an exhaust manifold pipe 24 connected tothe engine 12.

The engine 12 further includes an oil cooling system 26. The oil coolingsystem 26 includes an oil pump 28 for circulating the hot lubricatingoil of the engine 12 to an oil cooler 30 and the connecting lines 32 and34 to provide a path for the continuous circulation of the oil from theengine 12 to the oil cooler 30 and back to the engine 12.

The system 10 includes a source of pressurized fluid, such as a pump 40.The pump 40 draws a fluid, such as water, from a reservoir 42 by way ofa conduit 44. A fluid polisher 46 is provided in the line 44 and isadapted to remove minerals and other deposits from the water. A source48 of make-up water is provided to replenish the water in the reservoir42 if it becomes low.

A means 50 is provided for preheating the water from the pump 40. Thepreheating means 50 includes the oil cooling system 26 and a housing 52having a first fluid passageway 54 connected to the pump 40 by a conduit56. A relief valve 57 is connected to the conduit 56 and controls themaximum pressure of the fluid in the conduit 56. The housing 52 islocated in the conduit 32 of the oil cooling system 26 and defines asecond fluid passageway 58 interconnecting the conduit 32 within thehousing 52. The second fluid passageway is operatively associated inheat transferring relation with the first fluid passageway and isadapted to transfer the heat energy in the hot oil from the engine 12 tothe water passing through the first fluid passageway 54.

A first heat exchanger 60 is connected to the preheating means 50 by aconduit 62. The first heat exchanger includes an inlet port 64, anoutlet port 66, and an evaporator 68. The evaporator has a first fluidpassageway 70 connected between the inlet port 64 and the outlet port66. A second fluid passageway 72 is located in the evaporator 68 andconnected to the cooling lines 22 so that the pump 18 continuouslycirculates the engine cooling fluid. The second fluid passageway 72 isoperatively associated in heat transferring relation with the firstfluid passageway 70 so that the heat energy in the engine cooling fluidin the second fluid passageway 72 is transferred to the fluid or waterin the first fluid passageway 70. This heat energy is sufficiently highto convert the water in the first fluid passageway 70 to a steam.

A second heat exchanger 74 has an inlet port 76 and an outlet port 78and is located in the exhaust manifold pipe 24. A conduit 80 connectsthe inlet port of the second heat exchanger 74 with the outlet port 66of the first heat exchanger 60.

A third heat exchanger 82 has an inlet port 84 and an outlet port 86 andis also located in the exhaust manifold pipe 24. A conduit 88 connectsthe inlet port 84 of the third heat exchanger 82 with the conduit 62.

A first means 90 is provided for controllably directing a portion of thepreheated water at a preselected pressure to the inlet port 64 of thefirst heat exchanger 60 so that the preheated fluid is converted to asteam or gas at substantially the preselected pressure and forsubsequently directing the steam from the outlet port 66 of the firstheat exchanger 60 to the inlet port 76 of the second heat exchanger 74so that the steam at the preselected pressure is superheated to apreselected temperature. The first means 90 for controllably directlyincludes a flow control valve 92 operatively connected in the conduit 62between the inlet port 64 of the first heat exchanger and the point ofconnection of the conduit 88 with the conduit 62.

A second means 94 is provided for controllably directing the otherportion of the preheated water, at a preselected pressure higher thanthe preselected pressure of the preheated water from the first means 90,to the inlet port 84 of the third heat exchanger 82 so that the otherportion of the preheated fluid is converted to a steam at the higherpreselected pressure and superheated to a preselected temperature higherthan the temperature of the steam from the first means 90. The secondmeans for controllably directing includes a second flow control valve 96located in the conduit 88.

A dual pressure turbine 100 is provided in the heat recovery system 10and includes a housing 101 having a first inlet port 102 connected tothe outlet port 86 of the third heat exchanger 82 by a conduit 104, asecond inlet port 106 connected to the outlet port 78 of the second heatexchanger by a conduit 108, and an outlet port 110 connected to acondenser 112 by a conduit 114. The condensed fluid from the condenser112 returns directly to the reservoir 42 for reuse in the heat recoverysystem 10.

An output shaft 116 connects the dual pressure turbine 100 to a commonload 118 that is also driven by the engine 12.

As is best shown in FIG. 2, a first stage 120 is located in the housing101 and includes a first rotor chamber 122, a first rotor 124 rotatablypositioned in the first rotor chamber 122, a first plurality of blades126 evenly spaced and secured around the outer periphery of the rotor124, a first plurality of nozzles 128 interconnecting the first inletport 102 and the first rotor chamber 122, and an outlet passage 130.

For ease of illustration, a nozzle 132 is shown in FIG. 2 rotated 90°out of location. The nozzle 132 as illustrated should be rotated 90° tobe positioned in the top plane as properly illustrated in FIG. 4. Eachnozzle 132 of the plurality of nozzles 128, as better illustrated inFIG. 4 has a bellmouth inlet 134 formed by a radius of curvature equalto 1/2 the diameter of a throat portion 136. The throat portion 136 hasan axial straight length equal to 1/2 the diameter of the throat. Anoutlet portion 138 has a conical surface with an included angle ofapproximately 10°. As further illustrated in FIGS. 2 and 3, the outletportion 138 of each nozzle 132 opens into the first rotor chamber 122.The plurality of nozzles 128 cover an arc of approximately 136° and openinto the first rotor chamber 122 adjacent the plurality of blades 126.

Each blade 140 of the plurality of blades 126 are shaped such that apassage 142 between each pair of blades is of a constant width. Theheight and width of each blade 140 is substantially the same as theheight of the minor diameter of each of the outlet portions 138 of theplurality of nozzles 128.

A second stage 150 is located in the housing 101 and includes a secondrotor chamber 152, a second rotor 154 rotatably positioned in the secondrotor chamber 152, a second plurality of blades 156 evenly spaced andsecued around the periphery of the second rotor 154, a second pluralityof evenly spaced nozzles 158 opening into the second rotor chamber 152adjacent the second plurality of blades, and an outlet passage 160.

A first passage means 162 is provided for connecting the second inletport 106 with the second plurality of nozzles 158 so that the steam froma source, such as the second heat exchanger 74, is substantially axiallydirected to a first portion of the nozzles of the second plurality ofnozzles 158 at a predetermined velocity. The first passage means 162, asbetter illustrated in FIGS. 5 and 6, includes an arcuate slot 164connected to the second inlet port 106. At the area of connection withthe second inlet port 106, the arcuate slot 164 has a predeterminedcross-sectional area and defines an arc of approximately 200°. thecross-sectional area decreases as the arcuate slot 164 extends towardsthe second plurality of nozzles 158. The 200° angle of arc remainssubstantially constant and the arcuate slot opens to the secondplurality of nozzles 158 in a substantially axial direction.

A second passage means 170 is provided for connecting the outlet passage130 of the first stage 120 with the other portion of nozzles of thesecond plurality of nozzles 158 so that the steam from the outletpassage 130 of the first stage 120 is substantially axially directed tothe other portion of the plurality of nozzles 158 at substantially thesame velocity as the predetermined velocity of the steam from the secondinlet port 106. The second passage means 170, as better illustrated inFIGS. 5 and 6, includes an arcuate slot 172 connected to the outletpassage 130 of the first stage 120. At the area of connection with theoutlet passage 130, the arcuate slot 172 has a predeterminedcross-sectional area and defines an arc of approximately 160°. Thecross-sectional area increases as the arcuate slot 172 extends towardsthe second plurality of nozzles 158. The 160° angle of arc remainssubstantially constant and the arcuate slot 172 extends towards thesecond plurality of nozzles 158 in a substantially axial direction.

A third stage 180 is located in the housing 101 and includes a thirdrotor chamber 182, a third rotor 184 rotatably positioned in the thirdrotor chamber 182, a third plurality of blades 186 evenly spaced andsecured around the periphery of the third rotor, a third plurality ofevenly spaced nozzles 188 connected to the outlet passage 160 of thesecond stage 150 and opening into the third rotor chamber 182 adjacentthe third plurality of blades, and an outlet passage 190 connected tothe outlet port 110.

It is recognized that various types of fluids could be used in this heatrecovery system without departing from the essence of the invention, butpreferably water is used due to its availability and ability to absorblarge amounts of heat energy.

INDUSTRIAL APPLICABILITY

During operation of the heat recovery system 10, water from thereservoir 42 is drawn into the pump 40 and directed into the conduit 56at a predetermined pressure level of for example 2140 kPa (310 psi) asestablished by the relief valve 57. The polisher 46 sufficiently cleansthe water so that no impurities or other deposits are allowed to passthrough. These deposits, if allowed to pass through would possibly causelime or other deposits to form in the system thus reducing the overallefficiency of the heat recovery system.

The pressurized water in conduit 56 flows through the first passageway54 of the preheating means 50 and is preheated by the hot oil in thelubrication system. Due to the temperature of the oil, the water in thefirst passageway 54 is preheated to approximately 105° C. (220° F.).Because the water in the conduit 56 is under pressure, it does notconvert to steam.

The preheated water is directed to the evaporator 68 of the first heatexchanger 60 by the conduit 62. The flow control valve 92 in the conduit62 controls the flow entering the first heat exchanger 60 and alsocontrols the pressure of the fluid to approximately 130 kPa (19 psi). Asthe preheated water passes through the first fluid passageway 70 of theevaporator 68, the heat in the second fluid passageway 72 from thejacket water of the engine 12 adds heat energy to the water and convertsthe water to steam. Since the temperature of the fluid in the waterjacket is approximately 121° C. (250° F.) and the pressure of the fluidis approximately 130 kPa, the water is converted to steam and exits at121° C. and 130 kPa. The steam from the first heat exchanger 60 isdirected to the second heat exchanger 74 where it is superheated to atemperature of approximately 182° C. (360° F.).

The exhaust from the engine 12 is used to superheat the steam in thesecond heat exchanger 74. The temperature of the exhaust as it leavesthe engine 12 is approximately 460° C. (860° F.). By sizing the secondheat exchanger 74, the steam is superheated to a predeterminedtemperature and maintained at the predetermined pressure level of 130kPa.

The other portion of the preheated water in conduit 62 is directed tothe third heat exchanger 82 through the conduit 88. The flow controlvalve 96 in the conduit controls the flow entering the third heatexchanger 82 and also controls the pressure of the fluid toapproximately 1724 kPa (250 psi). By properly sizing the third heatexchanger 82, the preheated water entering the third heat exchanger 82is converted to steam and superheated to approximately 415° C. (780° F.)and maintained at the 1724 kPa pressure level.

After passing across both the second and third heat exchangers 74,82,sufficient heat energy in the exhaust has been used so that thetemperature of the exhaust as it leaves the exhaust manifold pipe isapproximately 204° C. (400° F.).

By using the heat energy in the oil cooling system 26 to preheat thewater from the pump 40 and by using the heat energy in the jacket waterof the engine 72 to convert some of the preheated water to steam, thenthe heat energy in the exhaust system is sufficient to convert theremainder of the water to steam and to superheat both quantities ofsteam to their respective preselected temperatures. This arrangementprovides the greatest effective use of the potential heat energy fromthe engine 12. Furthermore, since the heat energy from the jacket wateris being dissipated, a radiator normally will not be required in thesystem. By ensuring that the temperature of all fluids entering thesecond and third heat exchangers 74,82 are above a preselected level,the problems of sooting and oxide formations are greatly reduced. Thishelps both the efficiency of the system and the life of the elements ofthe second and third heat exchangers 74,82 located in the exhaust system16.

The dual pressure turbine 100 is used to convert the superheated steaminto useful work. The superheated steam at 460° C. and 1724 kPa isconnected to the first inlet port 102 of the dual pressure turbine 100and the superheated steam at 121° C. and 130 kPa is connected to thesecond inlet port 106.

The superheated steam in the first inlet port 102 is directed into thefirst rotor chamber 122 through the first plurality of nozzles 128.Based on the volume of superheated steam produced and the pressurethereof, nine nozzles 132 are used to direct the superheated steam tothe blades 126 of the first stage rotor 124.

Due to the shape of each of the nine nozzles, the velocity of the steamis increased such that the steam impinges the blades at supersonicspeed. It has been found that the highest efficiency of the first stageis attributed to the high velocity of the superheated steam, the veryclose spacing of the nozzle exits, and the controlled constant spacingbetween the blades 126 on the rotor 124. Furthermore, the height andwidth of each of the blades 126 is substantially the same as the heightof the minor diameter of each of the nozzle exits 138. Theserelationships provide a desired speed of 50,000 rpm.

The superheated steam leaves the blades 126 first stage rotor 124 at avelocity of approximately 137 m/sec (450 ft/sec), a temperature ofapproximately 182° C. (360° F.); and a pressure of approximately 130 kPa(19 psi). The pressure differential between the pressure of the steamentering the first stage 120 and the pressure of the steam leaving thefirst stage 120 results in a first stage turbine having a pressure ratioof approximately 13:1. The superheated steam enters the arcuate slot 172and is directed towards the second plurality of nozzles 158. Due to theincreasing cross-sectional area of the arcuate slot, the velocity of thesuperheated steam is decreased to approximately 76 m/sec (250 ft/sec)prior to entering the second plurality of nozzles 158. Because thearcuate angle of the arcuate slot 172 is approximately 160°, thesuperheated steam from the first stage is directed substantially only toa portion of the second plurality of nozzles 158 equal to the arcuateangle of the arcuate slot 172.

The superheated steam at the second inlet port 106 is communicated withthe second plurality of nozzles 158 through the arcuate slot 164. Thevelocity of the superheated steam at the second inlet port isapproximately 30 m/sec (100 ft/sec) and has a temperature ofapproximately 182° C. Since the cross-sectional area of the arcuate slot164 decreases in size as it extends towards the second plurality ofnozzles 158, the velocity of the steam is increased to approximately 76m/sec (250 ft/sec) prior to entering the second plurality of nozzles158. Because the arcuate angle of the arcuate slot 164 is approximately200°, the superheated steam from the second inlet port is directedsubstantially only to the other portion of the plurality of nozzles 158equal to the arcuate angle of the arcuate slot 164.

It is desirable that the superheated steam be directed into the secondplurality of nozzles 158 in a substantially axial direction in order togenerally eliminate turbulence in the steam flow. Furthermore, in orderto maximize the efficiency of the turbine 100, the respectivetemperature, pressure, and velocity of the superheated steam from thesecond inlet port 106 and the outlet passage 130 of the first stage 120should be substantially equal prior to entering the second plurality ofnozzles 158.

Wherein the first stage 120 is only a partial admission stage ofapproximately 37.8% admission, the second stage 150 is a full admissionstage receiving the superheated steam from two different sources. Thesuperheated steam exiting the second stage 150 enters the thirdplurality of nozzles 188 of the third full admission stage 180. Thesuperheated steam exiting the third stage 180 is connected to the outletport 110 and directed to the condenser 112 where it is condensed back towater and returned to the reservoir 42.

The heat recovery system 10 as described above provides a system havingan operating efficiency above 20% and the dual pressure turbine 100 inthe system has an operating efficiency above 80% and most effectivelyutilizes the heat energy produced by the engine 12 while limiting totalsize and controlling the cost. The three stage dual pressure turbine 100effectively utilizes the superheated steam produced from the heat energyin the entine 12 by using a first impulse stage having steam atsupersonic velocity impinging the blades of the first stage rotor.Furthermore the velocity of the steam exiting the first stage and thesteam entering the second inlet port is controlled so that when theyenter the second stage their velocities are substantially the same. Thesecond and third stages are full admission transonic reaction stages.The above three stage dual pressure turbine arrangement maintains thesuperheated steam in a superheated condition all the way through eachstage. If any droplets of water form while in any of the three stages,they would erode away material thus causing damage and shortening theeffective life of the dual pressure turbine.

Other aspects, objects and advantages of this invention can be obtainedfrom a study of the drawings, the disclosure and the appended claims.

What is claimed is:
 1. A heat recovery system for an engine having a liquid cooling system for transferring heat energy away from the engine and an exhaust system, comprising:a first heat exchanger having an inlet port and an outlet port and being located in heat transferring relation to the liquid cooling system; a second heat exchanger having an inlet port and an outlet port and being located in heat transferring relation to the exhaust system; a third heat exchanger having an inlet port and an outlet port and being located in heat transferring relation to the exhaust system; a source of pressurized fluid connected to the first and third heat exchangers; means for preheating the fluid from the source, said preheating means being located between the source and the first and third heat exchangers; first means for controllably directing a portion of the preheated fluid at a preselected pressure to the inlet port of the first heat exchanger so that the preheated fluid is converted to a gas at the preselected pressure and for subsequently directing the gas from the outlet port of the first heat exchanger to the inlet port of the second heat exchanger so that the gas at the preselected pressure is superheated to a preselected temperature; second means for controllably directing the other portion of the preheated fluid, at a preselected pressure higher than the preselected pressure of the fluid from the first means, to the inlet port of the third heat exchanger so that the other portion of the preheated fluid is converted to a gas at the higher preselected pressure and superheated to a preselected temperature higher than the temperature of the gas from the first means; and a dual pressure turbine having a high temperature and high pressure inlet port connected to the outlet port of the third heat exchanger, a low temperature and low pressure inlet port connected to the outlet port of the second heat exchanger, an outlet port connected to a condenser adapted to convert the outlet gas to a fluid, and an output shaft adapted to transmit a working force from the dual pressure turbine in response to the superheated gases from the respective second and third heat exchangers being directed therethrough.
 2. The heat recovery system, as set forth in claim 1, wherein the first heat exchanger includes an evaporator having a first fluid passageway connected between the inlet port and the outlet port of the first heat exchanger and a second fluid passageway operatively associated in heat transferring relation with the first fluid passageway and connected to the liquid cooling system so that the heat energy in the fluid being conduction from the engine through the second fluid passageway heats the fluid entering the first fluid passageway and converts the fluid to a gas.
 3. The heat recovery system, as set forth in claim 2 wherein the first means includes a flow control valve adapted to control the rate of flow and the pressure level of the flow to evaporator of the first heat exchanger.
 4. The heat recovery system, as set forth in claim 3, wherein the preheating means includes a housing having a first fluid passageway to pass the source of pressurized fluid through and a second fluid passageway operatively associated in heat transferring relation with the first fluid passageway and connected to an oil cooling system so that the oil in the oil cooling system carries the heat energy through the second fluid passageway of the preheating means and heats the fluid flowing in the first fluid passageway to a preselected temperature.
 5. The heat recovery system, as set forth in claim 4, wherein the second valve means includes a second flow control valve adapted to control the rate of flow and the pressure level of the flow from the source of pressurized fluid.
 6. The heat recovery system, as set forth in claim 5, wherein the engine is an internal combustion engine.
 7. The heat recovery system, as set forth in claim 6, wherein the internal combustion engine is a compression ignition type.
 8. The heat recovery system, as set forth in claim 7, wherein the fluid from the source is water and the gas is a steam.
 9. The heat recovery system, as set forth in claim 1 wherein the dual pressure turbine includes a housing having a first stage disposed therein, the first stage includes a rotor having a plurality of blades secured around the periphery and being rotatably positioned in a rotor chamber, the high temperature and high pressure inlet port, an outlet passage connected to the rotor chamber and a plurality of nozzles interconnecting the high temperature and high pressure inlet port with the rotor chamber adjacent a preselected number of blades of the plurality of blades, said plurality of nozzles being adapted to increase the velocity of the high temperature and high pressure gas so that the gas impinges the plurality of blades at a supersonic velocity.
 10. The heat recovery system, as set forth in claim 9, wherein the dual pressure turbine further includes a second stage disposed in the housing, the second stage includes a second rotor having a second plurality of blades secured around the periphery and being rotatably positioned in a second rotor chamber, the low pressure and low temperature inlet port, and a second plurality of nozzles opening into the second rotor chamber adjacent the plurality of blades and being evenly spaced therearound.
 11. The heat recovery system, as set forth in claim 10, wherein the dual pressure turbine includes passage means for communicating the low temperature and low pressure of the gas at the inlet port with a portion of the second plurality of nozzles so that the low temperature and low pressure gas is substantially axially directed to the portion of nozzles at a predetermined velocity.
 12. The heat recovery system, as set forth in claim 11, wherein the dual pressure turbine includes second passage means for communicating the gas at the outlet passage of the first stage with another portion of the plurality of nozzles so that the gas from the outlet passage of the first stage is substantially axially directed to another portion of the plurality of nozzles at substantially the same velocity as the predetermined velocity of the gas from the low temperature and low pressure inlet port.
 13. The heat recovery system, as set forth in claim 12 wherein the first passage means includes an arcuate slot defined in the housing connecting the low temperature and low pressure inlet port with the portion of nozzles of the plurality of nozzles, said arcuate slot defines an arc of approximately 200°.
 14. The heat recovery system, as set forth in claim 13, wherein the second passage means includes an arcuate slot defined in the housing connecting the outlet passage of the first stage with another portion of nozzles of the second plurality of nozzles, said arcuate slot of the second passage means being substantially axially located in the housing and defines an arc of approximately 160°. 